Debunking the 3 Biggest Exercise Myths

PM Contributing editor Alex Hutchinson is the author of Which Comes First, Cardio or Weights, a compendium of fitness misconceptions. Here, he lists why three commonly held exercise beliefs are dead wrong.

Stretching Prepares Your Body for Exercise

Stretching Prepares Your Body for Exercise

Stretching before exercise is a sacred ritual, but researchers have been finding that it actually slows you down. Florida State researchers recently showed that stretching before a run makes you about 5 percent less efficient, meaning you have to burn more energy to run at the same pace. This year, Italian researchers studying cyclists discovered why stretching is counterproductive. They found evidence that toe-touching stretches change the force-transmission properties of muscle fibers and alter the brain signals to muscle, reducing exercise efficiency by about 4 percent. Furthermore, there's insufficient scientific evidence that pre-exercise stretching reduces injury risk.

Loss of More than 2 Percent of Your Body Weight During Exercise Degrades Performance

Loss of More than 2 Percent of Your Body Weight During Exercise Degrades Performance

This debate, popular among exercise gurus and professional trainers, centers on how much water weight an athlete can lose without sacrificing performance. Lab tests have suggested that a body-weight loss of more than 2 percent impairs athletic performance. This information has become accepted. But a study of marathon runners in France published late last year found exactly the opposite. The fastest finishers were the most dehydrated, having lost 3.1 percent of their body weight, while the slowest finishers lost only 1.8 percent. It turns out that the body has hidden reservoirs that can generate several pints of water during exercise. For example, when your body burns fat or carbohydrates to fuel muscles, one of the byproducts is H2O. So drinking water when thirsty—and no more—is the best course of action.